The rate at which an intravenous fluid, such as blood, a nutritive solution, or a Ringer's solution, is to be administered to a patient depends upon such factors as the particular kind of operation to be performed on the patient, the seriousness of the patient's illness or injury, or the patient's pulse rate, blood pressure or heart condition. For example, 500 milliliters of intravenous fluid are usually administered in 1 to 3 hours, but are sometimes administered in 4 or 5 hours.
A conventional dripping apparatus is shown in FIG. 5. A vial 10 filled with an intravenous fluid is hung upside down on a stand (not shown). The vial 10 is stopped by a cork plug 12. A needle projecting upward from a tube 14 is inserted into the cork plug 12. The fluid flows through the needle into the tube 14. A drip-feed bottle 18 is connected to the lower end of the tube 14. The fluid that has flowed into the tube 14 drips into the drip-feed bottle 18, and remains there for a certain period of time. In the bottle 18 air bubbles are separated from the fluid. A vinyl tubing 20 is connected to the lower end of the bottle 18. An intravenous needle 32 is connected to the lower end of the vinyl tubing 20. From the bottle 18, drips of the fluid flow through the tubing 20 into the intravenous needle 32. A roller clamp 26 is connected to the vinyl tube 20. One can constrict the tubing 20 by operating the roller clamp 26. By constricting the tubing 20 or releasing it from constriction, he or she can control the rate of dripping of the fluid into the bottle 18 and, hence, the rate at which drips of the fluid are administered into a vein of the patient. However, the roller clamp 26 is operated manually and, hence, it is not easy to accurately control the rate of dripping of the fluid.
Use of a phototube has been proposed to provide a more accurate control. That is, it has been proposed that one detect the dripping of the fluid into the bottle 18 with a phototube and control the rate of dripping based on the detection thereof. This method, however, is disturbed if a shadow is accidentally thrown on the bottle 18. In addition, this method must be adjusted, through slightly, according to the kind of intravenous fluid used. Moreover, it is necessary to locate the phototube perpendicular to the direction of dripping of the fluid and, hence, it takes a relatively long time to make preparations for this method.